This invention relates generally to improved processes for preparing squaraine compositions, and more specifically, the present invention is directed to processes for obtaining squaraine compositions with reduced dark decay characteristics, and increased charge acceptance properties, as compared to squaraines prepared from the known squaric acid processes. In one embodiment of the present invention there is provided certain known squaraine compositions of reduced dark decay characteristics, and increased charge acceptance, when these compositions are incorporated into photoconductive devices, with a process which is effected by the reaction of squaric acid and an aromatic aniline in the presence of aliphatic amines, particularly those aliphatic amines with a carbon chain length of from about 4 to about 20 carbon atoms. The squaraine compositions resulting are useful for incorporation into layered photoresponsive imaging devices which are sensitive to light in the wavelength region of from about 400 to about 1,000 nanometers. Accordingly, the resulting devices are responsive to visible light, and infrared illumination needed for laser printing, wherein for example, gallium arsenide diode lasers are selected. The specific photoresponsive device envisioned can, for example, contain situated between a photogenerating layer and a hole transport layer, or situated between a photogenerating layer, and a supporting substrate, a photoconductive composition, comprised of the squaraine compositions prepared in accordance with the process of the present invention.
Photoconductive imaging members containing specific squaraine compositions, particularly hydroxy squaraines, are well known. Moreover, the use of certain squaraine pigments in photoresponsive imaging devices is disclosed in a copending application, wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device, there can be selected various squaraine pigments, including hydroxy squaraine composition. Additionally, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
In another copending application, there is described novel squaraine compositions of matter, such as bis-9-(8-hydroxyjulolidinyl)squaraine, and the use of these compositions as imaging members. One of the imaging members contains a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which compositions are comprised of the novel julolidinyl squaraines materials disclosed in the copending application, and a hole transport layer.
Disclosed in U.S. Pat. No. 3,617,270 are optically sensitized photoconductive layers which preferably contain zinc oxide as a photoconductor, the sensitivity of which remains unchanged as a result of storage, in view of the presence of 1,3 or 1,2-squaric acid methine dyes of the formula as illustrated in column 1, begining at line 35; while U.S. Pat. No. 3,824,099, discloses sensitive xerographic devices containing a charge generating layer comprising a squaric acid methine dye, and a charge transport layer containing a tri-arylpyrazoline compound. Also known are layered photoresponsive devices with photogenerating layers and transport layers, reference U.S. Pat. No. 4,265,990. Examples of photogenerating layers disclosed in this patent include trigonal selenium, and phthalocyanines, while examples of transport layers that may be selected are comprised of certain diamines dispersed in an inactive resinous binder composition.
Processes for preparing squaraine compositions generally involve the reaction of squaric acid with an amine. Thus, for example, the novel julolidinyl squaraine compositions disclosed in the referenced copending application are prepared by the reaction at a temperature of from about 50 degrees Centigrade to about 130 degrees Centigrade of an aromatic amine and squaric acid, in a molar ratio of from about 1.5:1 to 3:1, in the presence of a mixture of an aliphatic alcohol and an optional azeotropic cosolvent. About 200 milliliters of alcohol per 0.1 mole of squaric acid are used, while from about 40 milliliters to about 4,000 milliliters of azeotropic material are selected. Illustrative examples of amine reactants include 8-hydroxyjulolidine, while examples of aliphatic alcohols selected include 1-butanol. Azeotropic materials used include aromatic compositions such as benzene and toluene.
Moreover, disclosed in U.S. Pat. No. 4,390,610, are imaging devices sensitive to the output of gallium arsenide lasers, the devices containing a polycarbonate polymer adhesive layer coating on an electrically conductive substrate, a first charge generating layer and a second charge generating layer of a hydroxy squarylium material, and a top overcoating charge transport layer. As indicated in the background disclosure of this patent, reference Column 2, beginning at line 4, prior art layered photoconductors are not entirely acceptable in the areas of light fatigue, dark fatigue, and dark decay. Similar teachings are contained in U.S. Pat. Nos. 4,353,971 and 4,391,888. These problems of high dark decay and low charge acceptance are eliminated with the squaraine compositions prepared in accordance with the process of the present invention as detailed hereinafter.
While the above processes for preparing squaraine compositions are suitable for their intended purposes, there continues to be a need for other processes wherein photoconductive squaraine compositions can be prepared. Additionally, there remains a need for simple, economical processes for preparing squaraine compositions which when incorporated into photoconductive devices, result in reduced dark decay and increased charge acceptance as compared to substantially similar squaraine compositions resulting from the squaric acid process. Further, there continues to be a need for the preparation of squaraine compositions of enhanced photosensitivity when these compositions are selected for layered photoresponsive imaging devices. Moreover, there remains a need for improved processes for preparing various known squaraine compositions which when incorporated into imaging members exhibit excellent dark decay properties, and high charge acceptance values.